{
  "bibcode": "2020GCN.26966....1Z",
  "body": "The Zwicky Transient Facility (ZTF; ATel #11266) reports the discovery of\nZTF20aajnksq, a rapidly fading red transient located at\n12:47:04.87 +45:12:02.3 (J2000)\n191.770292 +45.200626 (J2000)\nand detected as part of the ZTF Uniform Depth Survey (Goldstein et al. in\nprep).\n\nThe source was discovered on UT 2020-01-28T06:43:20.640 at r=19.6 mag,\nwhich was 0.74 days after the last non-detection. Follow-up photometry with\nthe IO:O optical imager on the Liverpool Telescope (PI: D. Perley) and the\nWafer-Scale Imager for Prime (WASP) on the 200-inch Hale telescope (PI: I.\nAndreoni) at Palomar Observatory established a rapid fade rate of 2.5\nmagnitudes in 1.25 days as well as red colors (g-r=+0.65, from the WASP\nobservation).\n\nWe obtained a target-of-opportunity (PI: M. M. Kasliwal) spectrum with the\nLow Resolution Imaging Spectrometer (LRIS) on the Keck I 10-m telescope,\nwhich showed features consistent with the Lyman break and Lyman alpha\nabsorption at z=2.9.\n\nWe obtained a target-of-opportunity observation with the Neil Gehrels Swift\nObservatory (Swift) and detected X-ray emission at 0.0039 ct/s. Assuming a\nneutral hydrogen column density n_H = 1.77E20/cm2 and a power-law spectrum\nwith photon index 2, the unabsorbed flux is 1.5E-13 erg/cm^2/s,\ncorresponding to a luminosity of 1.1E46 erg/s.\n\nWe searched the Fermi/GBM catalog and identified a reported likely short\nGRB 24 degrees away: GRB 200128A (GCN #26909). ZTF20aajnksq is located\nalong the 90% contour of the localization region. The trigger time of GRB\n200128A is three hours before the first optical detection.\n\nWe are grateful to the staff of Palomar and Keck for rapidly scheduling our\nobservations, and to M. Heida (ESO Garching) and J. Rhoads (Goddard) for\naccommodating the interruption to their scheduled programs. Thank you to\nthe Swift team for rapidly scheduling and executing our observations.\n\nZTF is a project led by PI S. R. Kulkarni at Caltech (see ATEL #11266), and\nincludes IPAC; WIS, Israel; OKC, Sweden; JSI/UMd, USA; UW,USA; DESY,\nGermany; NRC, Taiwan; UW Milwaukee, USA and LANL USA. ZTF acknowledges the\ngenerous support of the NSF under AST MSIP Grant No 1440341. Alert\ndistribution service provided by DIRAC@UW. Alert filtering is being\nundertaken by the GROWTH marshal system, supported by NSF PIRE grant\n1545949.",
  "circularId": 26966,
  "createdOn": 1580680390000,
  "email": "annayqho@gmail.com",
  "subject": "ZTF Discovery of ZTF20aajnksq: a Rapidly Fading Luminous Transient in the GRB 200128A Localiziation Region",
  "submitter": "Anna Ho at Caltech  <annayqho@gmail.com>",
  "eventId": "GRB 200128A"
}